Many proposals were made in the past, for the purpose of improving mechanical strength of catalyst, in respect of those catalysts used in production of acrolein and/or acrylic acid by catalytic vapor-phase oxidation of propylene in the presence of molecular oxygen or those used in production of methacrolein and/or methacrylic acid by catalytic vapor-phase oxidation of isobutylene or TBA.
Those proposals include, for example, a supported catalyst in which whiskers having an average diameter of not more than 1 μm are used as a carrier assistant (cf. JP 59 (1984)-173140A); a supported catalyst comprising molybdenum and bismuth as the essential ingredients, in which inorganic fibers having an average diameter of 2-200 μm are used as a carrier assistant (cf. JP 06 (1994)-381A); a ring-formed catalyst comprising molybdenum and bismuth as the essential ingredients, which also contains inorganic fibers (cf. JP 2002-273229 A); and a method of packing solid catalysts differing in mechanical strength, by dropping them by the order of their mechanical strengths from high to low, in which the amount of inorganic reinforcing agent such as inorganic fibers or whiskers is adjusted as one of the means for obtaining a catalyst of high mechanical strength (cf. JP 2004-82099A).